The present invention relates to the piloting or flight of aircraft and concerns a flight process "by maintaining the speed by action on the elevator". It solely relates to the flying of aircraft during an altitude change, e.g. when cruising or during climbing or descending phases. During altitude changes it is directed at acquiring and/or maintaining a nominal speed, which is necessary and important in view of the fundamental function of the speed which, for safety reasons, must always be equal to or between the minimum speed authorized and the maximum speed authorized by the designer.
It applies both in the case of automatic piloting without any intervention on the part of the crew and to manual piloting by the crew using the control column and following the lines or bars of the flight director. It is pointed out that the flight director is an instrument essential to piloting and which displays on the instrument panel with the aid of two perpendicular and mobile bars on a dial, one horizontal relating to the vertical guidance and the other vertical relating to the lateral guidance, the variation between the real trajectory or path of the aircraft and the ideal trajectory or path calculated on the basis of flight instructions. Piloting, whether automatic or manual, consists of acting on the controls of the apparatus in order to permanently maintain the intersection point of these two bars or lines in the centre of the dial. The present invention only relates to the vertical guidance and therefore only the horizontal bar is to be taken into consideration within the scope of the present process.
In the present text, generally no details are given of whether it is automatic or manual piloting, because the process according to the invention functions equally well in both cases. Thus, the computer producing the piloting or flight rule or law on the basis of the flight parameters can transmit instructions directly to the elevator (autopilot) and to the flight director (manual flight), which places the bars at the location corresponding to the path to be followed, so that in turn the pilot acts on the controls so as to place and maintain the intersection point of the bars in the centre of the dial.
It is also pointed out that the elevator, located to the rear of the apparatus and whose position is controlled by the control column or the power member of the autopilot, makes it possible to regulate the path of the aircraft with respect to a horizontal plane. It evolves between so-called "nose up" positions bringing about an aircraft climb and so-called "dive" positions, bringing about the descent of the aircraft. It therefore plays an essential part in the process according to the invention during which, by definition, the aircraft changes altitude.
After giving these basic notions, consideration will now be given to the following points. In order to modify the aircraft speed, the automatic or manual pilot has two essential parameters:
a) the thrust of the engines, which is the only internal energy source of the aircraft; PA1 b) exchanges between the kinetic energy and the potential energy of the aircraft. PA1 either the thrust of the engines is constant (in general at maximum power if the aircraft climbs and at idling speed if the aircraft descends) and the maintenance of the nominal speed takes place by action on the elevator, so that the aircraft takes the optimum gradient descending or climbing path; PA1 or the nominal speed is obtained by the continuous regulation of the engine thrust, the automatic or manual pilot through the flight regulator only regulating the nominal magnitudes other than the speed. PA1 a first sequence during which the elevator only receives an instruction to put the nose up (on climbing) or dive (on descending) and priority is given to said elevator by transmitting to the engine automatic thrust control member a nominal speed equal to or higher than the instantaneous speed of the aircraft on climbing, or equal to or below the instantaneous speed of the aircraft on descending, so that said thrust continuously increases on climbing or continuously decreases on descending until the maximum thrust is obtained in the first case and the minimum thrust in the second and PA1 a second sequence, following the first, during which the real nominal speed is supplied to the elevator instruction computer and said same nominal speed, increased (when climbing) or decreased (when descending) by a margin is supplied to the automatic thrust control member.
Thus, the pilot can act on the speed both by modifying the thrust of the engines and by modifying, with the aid of the control column the position of the elevator without modifying the engine thrust.
In the hitherto used flight or piloting processes, the maintaining of a nominal speed takes place with the aid of two different methods, which are exclusive of one another, i.e. which are never used together:
In the hitherto used piloting methods, the maintaining of a nominal speed during altitude changes takes place according to the first of the two aforementioned methods and namely by the action on the elevator.
In these known procedures, the maintaining of the nominal speed, both with autopilot or manual pilot with the flight director by controlling the aircraft trajectory, takes place by using the elevator.
On the basis of these informations supplied by on-board transducers (speed, gradient, acceleration, etc.) and the value of the nominal speed to be reached, the computer applies the piloting rule and produces either the autopilot elevator instruction, or the displacement instruction for the horizontal bar of the flight director which the pilot will centre on the dial of the instrument panel by varying the aircraft attitude by means of the control column and the elevator.
The use of this piloting rule makes it possible to carry out the following. If the nominal altitude displayed by the crew exceeds the actual altitude of the aircraft it is necessary to climb and the engine thrust is generally brought to a maximum and the piloting rule makes it possible to arrive at and maintain the nominal speed. If the nominal altitude is below the actual altitude of the aircraft, it is necessary to descend and generally thrust is reduced to idling power and the piloting rule acquires and maintains the nominal speed, as when climbing, by controlling the optimum descent gradient.
It can be seen that in this operating procedure there is no automatic regulation of the thrust as a function of the speed to be maintained. The automatic thrust regulation takes place on an "all or nothing" basis. It is the bringing to maximum or minimum thrust which brings about the response of the aircraft and the piloting rule merely makes the aircraft speed dependent on the nominal speed.
Although this piloting or flight procedure has been used up to now, it suffers from a certain number of disadvantages which will be described hereinafter and which require very special attention, particularly when flying in strong turbulence. In all flight phases, but particularly near to the ground (initial climb and approach), the speed of the aircraft is a very important parameter which the crew must be very carefully monitored.
When the speed is being maintained by the elevator, either in the case of autopilot or manual pilot with a flight director, the thrust is fixed and is generally idling during the descent phase. Any atmospheric disturbance (gust of wind) or when the flight director instructions are not carefully respected by the pilot, can then lead to the aircraft speed dropping below the nominal speed. This which can have dangerous consequences if the nominal speed is the minimum authorized speed, because the recovery of the necessary speed can only be made good in this case by increasing the descent gradient, or by wave-off with a relatively long engine response time.
Conversely, in the case of climbing at maximum speed, the thrust is generally fixed and at a maximum, so that for the same reasons as described hereinbefore (turbulence, not following the bars) can lead to the aircraft speed exceeding the maximum authorized speed.